As a display device employing a novel image display method replacing CRT (Cathode Ray Tube), there have been recently developed a liquid crystal display using a liquid crystal panel (LCD: Liquid Crystal Display), an EL display using a phenomenon of electro luminescence (EL: Electro Luminescence) and a plasma display using a plasma display panel (hereinafter referred to as PDP: Plasma Display Panel).
In the plasma display among those stated above, it is possible to achieve slim lightweight panels, simplification of the structure and large screens, and it is possible to observe a sharp image at an angle in a wide range upward and downward and on all sides, because a visible range, the so-called view angle can cover 160° or more both in the horizontal and vertical directions, when compared with a liquid crystal panel. Further, the plasma display is of an image display system with a fixed pixel by means of a dot matrix printer, and therefore, out of color registration and a distortion of an image area are controlled, and an image with high image quality can be depicted even when it is a large image area.
The PDP used for the plasma display is provided with a large number of discharge cells each being formed by two glass base boards provided with electrodes and by a partition provided between the base boards, and a phosphor layer on which a phosphor is coated is formed inside each discharge cell. The PDP constructed in this way is arranged so that vacuum ultraviolet (hereinafter referred to as VUV: Vacuum Ultraviolet) caused by discharge gas filled in a discharge cell may be generated when impressing voltage between electrodes to discharge the discharge cell selectively, and thereby, a phosphor may be excited to emit visible light.
As a general manufacturing method for the phosphor stated above, there are two ways including a solid phase synthesis wherein compounds containing an element constituting a phosphor matrix and compounds containing an activating element, each being in a prescribed amount are mixed, and then, are baked, and a liquid phase synthesis wherein a phosphor material solution containing an element constituting a phosphor matrix and a phosphor material solution containing an element of activating agents are mixed, and baking is carried out after sediment of precursors of the phosphors thus obtained is subjected to liquid-solid separation.
For realizing images which are more clear and are of higher image quality, PDP is highly miniaturized recently, and a phosphor which is small in size and has high light-emission intensity is required by the highly miniaturized PDP. However, a phosphor particle obtained through a solid phase synthesis is large in size, and has a problem that emission efficiency and light-emission intensity are lowered as its particle size turns out to be smaller.
On the other hand, there has been developed a method to miniaturize phosphor particles by conducting a crushing treatment process after manufacturing a phosphor by and a liquid phase synthesis, and thereby to improve light-emission intensity by receiving VUV efficiently. However, there is also caused a problem that the light-emission intensity is lowered, because a surface layer of the phosphor is damaged by the crushing treatment process, and distribution of particle sizes is broadened.
There is also caused another problem that impurities such as nonreacted substances and by-products adhere to the surface of phosphor particle after baking, to absorb VUV generated by electric discharge, resulting in a decline of light-emission intensity.
With the foregoing as a background, there have been developed a phosphor capable of improving emission efficiency of the phosphor, and a manufacturing method of the phosphor wherein impurities such as nonreacted substances and by-products adhering to the surface layer of damaged phosphor particles and to the surface of the phosphor particle are removed by conducting chemical processing by etching solutions such as nitric acid or hydrochloric acid on the phosphor surface, after the phosphor is synthesized by the liquid phase synthesis (for example, Patent Documents 1, 2 and 3).
(Patent Documents 1) TOKKAI No. 2000-226577
(Patent Documents 2) TOKKAI No. 2001-172622
(Patent Documents 3) TOKKAI No. 2003-292950